Computer chips contains milions and bilions of transistors packed together in a tiny substrate. Our brain is made of billions of nureon which acts as switches for our memory and logical reasoning.
Computer chips are made of neurons called transistors.
What is a transistor?
As a beginner you might be new to transistors, well transistors works on your phones, bluetooth devices, amplifiers, microphones and all other electronic devices.
Going straight to the point, transistors are electronic components made from semiconductor materials. They are made from junctions of semiconductor materials, which can be used for switching and amplification.
How do transistors works and what are they made of?
Transistors are made from semiconductors like silicon and germanium. Semiconductors are metals that behaves as a non-conductor of electricity in its purest form and behaves as conductor when doped with a foreign material.
To make semiconductors conductive they needed to be doped. The type of foreign elements added to them affects the way they conduct electricity. For example when arsenic or antimony is doped into silicon (a Semiconductor obtained from sand) it forms an N-TYPE semiconductor because there is much electrons than its holes(protons).
Also when boron or indium is doped into silicon or germanium it produces a P-TYPE semiconductor because its holes(proton) is much than its electrons.
Therefore there are two types of doped semiconductors;
- The N-TYPE
- P-TYPE.
When a P-TYPE is directly joined end to end to an N-TYPE it forms a P-N junction diode, the building block of the transistor. When a battery is connected to the junction diode with its positive polarity connected to the P-TYPE end and the negative polarity to the N-TYPE end, current flows in the circuit without any resistance, but when reversed it blocks current completely and behaves as an insulator.
Transistors are formed by sandwiching a P-TYPE in-between two N-TYPEs to forms a three terminals NPN transistor. Also when an N-TYPE is sandwiched into two P-TYPEs it forms a three terminals PNP transistors.
Types of transistors and their mode of operations.
There are basically two types of transistors classified according to their mode of operations and the way they are manufactured. Some are use in high voltage situations while some are used in low current applications, they are BJTs and FETs.
1.Bipolar junction transistors (BjT)
From its name it can be understood that it is the combinations of two different doped semiconductors which consists of two current carriers. It was invented in 1948 by William shockley, john bardeen and brattain. It has changed the world of electronics. It uses two carriers of electricity; electrons and holes.
It mainly amplifies and switches signals. It is made of three terminals; emmiter, base and collector.
For easy understanding a transistor looks like a sandwich which has meat puffed between its flesh. The emitter is the flesh on one side while the collector is also a flesh at the other side. The meat at the middle acts as the base.
Current flows from the emitter to the collector and while electrons flows from collector to the emitter.
The base controls the current flow.
There are two types of BJTs;
•Point contact.
it was the first transistor invented in 1947 by William Shockley, Walter Brattain and John Braeden. It emitter and collector are connected together with gold foil while the base is connected with a metal slab to an N-type germanium semiconductor.
•Junction contact.
it is more used than the point contact type. It is made from the direct Junction of base, emitter and collector without a metal junction, thus they are connected to each other directly.
There are two types of junction contact BJTs;
1. NPN.
It is made by sandwiching a P-type Semiconductor in between two N-types. It is the most used and available because it is easily produced from silicon. Electrons flows from the collector to the emmiter while current flows from emmiter to collector.
Working principle of NPN transistor.

The collector is always connected to positive terminal of a DC, while the emitter is connected to the negative terminal of a DC,the base is connected to either the collector or emitter with a resistor. When current is applied to it, the transistor is in OFF (0) state when the base current is the same with the emitter current. If the base current is increased than that of the emitter it stays in the ON (1) state.
2. PNP.
It is made by sandwiching an N-type semiconductor in between two P-types. Electrons flows from the emitter to the collector, while current flows from collector to the emmiter.
Working principle of PNP Transistors.
The emitter is connected to a negative DC terminal and its collector to the positive terminal DC. The base is connected to the emitter or collector with a resistor.The transistor is in the OFF state when the base voltage is the same as the emitter voltage. The transistor mode is in ON state when the base voltage decreases with respect to the emitter. By using this property the transistor can act on both applications like switch and amplifier
Other types of transistors based on BJT structure.
There are many other types of transistors which their construction is based on BJT structure they are;
*
1. Darlington transistors.
It is the combination of two bjt transistors in a single chip. It has three output terminals like a normal transistor. The first transistor amplifies current while the second one amplifies the current again thus it current gain can be around 1000 times. It was invented in 1953 by Sidney Darlington. It is commonly use for amplification.
2. Photo-transistors.
It is made of arsenide or galium produces current when. Strikes on it base to emitter junction. When light falls on the photo sensitive base, current flows from the emitter to the collector, the current produced is in miliamps.
3. Photo-darlington.
Two transistor combined together to form a darlington type is made sensitive to light. It produces electricity when exposed to an external light.
Circuit Applications of BJTs.
BJT transistors can be made to do two basic things in circuit they are;
*
1. For switching current and oscillation.
Transistors can switch signals and also amplify it at the same time.
Current flows from the emitter to the collector in the forward bias mode, it doesn't conduct electricity when their is no current at the base,it is in the off mode(2). It allows current to flow from the emitter to collector when current is applied to the base, thus it is in the on mode (1)
2. It is use for small signals and current amplification.
It works as an amplifier when it emitter is connected to a - polarity and the base is connected to a + polarity with a resistor. The base
Controls the amount of current flowing from the emitter to the collector. Small current flows from the voltage source to the base of the transistor. The current at the base turns on the transistor.
2. Field effects transistors (FETs).
They are three terminals transistors, which have three pins for connecting to circuits namely Gate, source anddrain. This types of transistors are used in high voltage situations. They are use for switching, amplification and in RF technology. FETs are called unipolar transistors because they have only one majority carrier, unlike BJTs which has two carriers ( electrons and holes).
There are two types of Field effect transistors depending on their majority carrier;
P-channel and N-channel.
In the P-channel, holes are the majority carrier while N-channel types have electrons as their majority carrier.
Categories of FETs are;
1. Junction field effect transistors (JFETs).
JFET is a field effect transistor, it has three terminals namely gate, source and drain. It has much numbers of applications like switching, amplification and RF generation circuits. It is also categoriesed into P-channel JFET and N-channel JFET.
2. Insulatedd gate field effect transistors (IGFETs).
These type of transistors had four terminals namely, Gate, body, source and drain. It gate is insulated from it channel.
An example of an IGFET is MOSFET. It has a full meaning of metalic oxide semiconductor field effect transistor. A metalic oxide is made the insulator of the gate from the channel.
Applications of FETs.
•For Switching.
FETs are use for switching because it can be fully operated either fully ON or fully OFF.
•Amplifiers.
They're use as power amplifiers because they have high current gain.
Tags:
Basic Electronics